Atmospheric dispersion, aerosols

Dispersion Normalization. Atmospheric dispersion is greater in winter than in summer in New York City and, in addition, varies from year to year. Thus, for a constantly emitting source of particles, atmospheric concentrations of TSP observed in winter would be lower than in summer. In order to relate ambient concentrations of particulate species to their sources Kleinman, et al. ( 5), suggested the use of a dispersion normalization technique based on the dispersion factor proposed by Holzworth ( ). Ambient concentrations of aerosol species are multiplied by the ratio of the dispersion factor for the sampling period to an average dispersion factor of 4200 m /sec. 

This chapter treats those aerosol phenomena that are known or believed to be important in atmospheric chemistry. For treatment of related, but specialized, topics, a number of excellent references are available. The classic works on aerosol physics are The Mechanics of Aerosols by the late N. A. Fuchs (1964) and Highly Dispersed Aerosols (Fuchs and Sutugin, 1970). The... 

Colloidal-sized particles in the atmosphere are called aerosols. Those formed by grinding up bulk matter are known as dispersion aerosols, whereas particles formed from chemical reactions... 

The dilution in air due to the atmospheric dispersion of radioactive aerosols resulting from a release of radioactive material was modelled for positions along the centre line of the plume using the diffusion equation with a top hat distribution to account for the directional fluctuations in crosswinds ... 

Condensation is the main route leading to the formation of finely dispersed aerosols in nature and industry. The formation of cumulus (composed of water droplets) and cirrus (composed of ice crystals) clouds mainly starts with heterogeneous nucleation on fine dusts and microcrystals of salt. These microcrystals form when splashes of sea water are dried and raised to high layers of atmosphere by convection air streams. 

The method for generating the required atmospheric dispersion of anti-ChE (e.g.. as vapor or aerosol). Highly volatile and/or reactive liquids may have to be metercd from stainless-stce cylinders (Dodd etal.. 1986). For generation of liquid aerosols of respirable size, the La,skin nebulizer is suitable for one-component test materials (Drew et at., 1978) and for generation of du.st particles, the Wright dust feeder is commonly used. 

Coarse mode particles (>2.5 pm diameter) tend to result from mechanical processes such as construction, traffic, combustion, and the soil lifted and dispersed by wind action. The main competing mechanisms determining the stability of this size range of particles are turbulent mixing and sedimentation. For typical coarse particles in the atmosphere, the aerosol residence times range from several hours to about a day [121]. 

Gas Dispersion. This group of models describes the atmospheric dispersion of clouds of gases and gas/aerosol mixtures. The objective of these models is to estimate the variation of concentration in air of the released material as a function of time and distance from release location. Further information can be found in CCPS (1995a). 

MODELING ATMOSPHERIC DISPERSION OF HEAVIER-THAN-AIR CLOUDS CONTAINING AEROSOL... 

Kukkonen, J. 1990. Modelling Source Terms for the Atmospheric Dispersion of Hazardous Substances, Commentationes Physico-Mathematicae 115, The Finnish Society of Sciences and Letters, Helsinki. Kukkonen, J., T. Vesala, and M. Kulmala. 1989. The Interdependence of Evaporation and Settling for Airborne Freely Falling Droplets, Journal of Aerosol Science, vol. 20, no. 7, pp. 749-763. Kukkonen, J., M. Kulmala, J. Nikmo, T. Vesala, D. M. Webber, and T. Wren. 1993. Aerosol Cloud Dispersion and the Suitability cf the Homogeneous Equilibrium Approximation, AEA Report AEA/ CS/HSE R 1003/R, Warrington, Cheshire. 

Entrainment The suspension of liquid as an aerosol in the atmospheric dispersion of a two-phase release or the aspiration of air into a jet discharge. 

DeVaull, G., J. A. King, R. J. Lantzy, and D. J. Fontaine (1995). An Atmospheric Dispersion Primer Accidental Releases of Gases, Vapors, Liquids, and Aerosols to the Environment. International Conftrence and Workshop on Modeling and Mitigating the Consequences (fAccidental Releases of Hazardous Materials. Sept. 26-29, New Orleans. New York American Institute of Chemical Engineers. 

To compare the differences in the relative dose impacts of and Pu fueled reactors without developing reactor specific accident scenarios, equivalent quantities of and 39pu were assumed to be released from a plant vent as aerosols as the result of an explosive release. Standard atmospheric dispersion factors, site boundaries, and dose factors were used for the calculations. 

Sulfolane causes minimal and transient eye and skin irritation (19,20). Inhalation of sulfolane vapors in a saturated atmosphere is not considered biologically significant. However, when aerosol dispersions have been used to elevate atmospheric concentration, blood changes and convulsions have been observed in laboratory animals (22,31). Convulsions caused by sulfolane injected intraperitoneaHy have also been studied (32). 

The Britter and McQuaid10 model was developed by performing a dimensional analysis and correlating existing data on dense cloud dispersion. The model is best suited for instantaneous or continuous ground-level releases of dense gases. The release is assumed to occur at ambient temperature and without aerosol or liquid droplet formation. Atmospheric stability was found to have little effect on the results and is not a part of the model. Most of the data came from dispersion tests in remote rural areas on mostly flat terrain. Thus the results are not applicable to areas where terrain effects are significant. 

A different approach which also starts from the characteristics of the emissions is able to deal with some of these difficulties. Aerosol properties can be described by means of distribution functions with respect to particle size and chemical composition. The distribution functions change with time and space as a result of various atmospheric processes, and the dynamics of the aerosol can be described mathematically by certain equations which take into account particle growth, coagulation and sedimentation (1, Chap. 10). These equations can be solved if the wind field, particle deposition velocity and rates of gas-to-particle conversion are known, to predict the properties of the aerosol downwind from emission sources. This approach is known as dispersion modeling. 

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